There’s one other typo that could be problematic if it’s not just erroneous transcription.

The event payload in the Elixir side has a key of login_token, but the object destructuring on the JS side’s handleEvent call is using the key login_tkn which would be undefined based on the payload coming across the socket.

If you are using push_event:

Phoenix Liveview adds the string phx: in front of the event name.
So "saveLoginToken" becomes "phx:saveLoginToken"

Have a look at

with the topic: Handling server-pushed events

let liveSocket = new LiveSocket(...)
window.addEventListener(`phx:highlight`, (e) => {
  let el = document.getElementById(e.detail.id)
  if(el) {
    // logic for highlighting
  }
})

Not sure if this is the reason for your problem

Thanks so much,

I put it this way, and it worked:

@impl true
  def handle_event("check_login_credentials", params, socket) do
    login_token = process_token_request(params["user_name"], params["password"], socket)

    send_token_to_browser(socket, params, login_token)
  end

  @impl true
  def send_token_to_browser(socket, params, login_token) do
    if login_token do
      socket = socket |> assign(:is_authenticated, true)
      {:noreply, push_event(socket, "save_login_token", %{payload: login_token})}
    else
      {:noreply, assign(socket, params: params)}
    end
  end